The present invention relates to an electrophotosensitive receptor, and more particularly to a novel electrophotosensitive receptor having an electrophotosensitive layer containing an azo compound, and further particularly it relates to a highspeed and highly durable electrophotosensitive receptor suitable for repetitive use.
As an electrophotosensitive receptor those having an electrophotosensitive layer consisting principally of such inorganic photoconductors as selenium, zinc oxide, cadmium sulfide or the like have been widely known. However, these are not necessarily satisfactory in respect of the sensitivity, thermal stability, moisture resistance and durability, and particularly, the use of selenium and cadmium sulfide has been restricted due to their toxicity.
On the other hand, an electrophotosensitive receptor having an electrophotosensitive layer consisting principally of an organic photoconductive compound have many such advantages that they can be readily manufactured, are inexpensive, can be easily handled and are generally excellent in the thermal stability as compared to selenium electrophotosensitive receptors, so that they have attracted attention recently.
As such an organic photosensitive compound, poly-N-vinyl carbazole is well known, and an electrophotosensitive receptor having an electrophotosensitive layer consisting principally of a charge-transfer complex formed from the above compound and such Lewis acids as 2,4,7-trinitro-9-fluorenone or the like has already been made practical reality. However, the electrophotosensitive receptor is not necessarily satisfactory in the speed and the durability.
On the other hand, a multilayered type electrophotosensitive receptor wherein the carrier-generating function and the carrier transport function are shared by different materials respectively or of the function separative type of the dispersion type have been known. Such function separative type photoreceptor has the advantages that they allow material for the functions to be selected in a wide range and that they permit to relatively readily prepare an electrophotosensitive receptor having such arbitrary properties as the charging property, speed, durability and the like. Various carrier generation materials or carrier transport materials using the above electrophotosensitive receptor have heretofore been proposed. For example, there have been made practical reality such an electrophotosensitive receptor as having an electrophotosensitive layer composed in combination of a carrier generation layer consisting of an amorphous selenium and a carrier transport layer consisting principally of poly-N-vinyl carbazole. However, the carrier generation layer consisting of amorphous selenium has the disadvantage that it has inferior thermal resistance.
And, the use of organic dye or pigment as the carrier generation material has been variously proposed, for example, electrophotosensitive layers containing a monoazo compound or bisazo compound is already in the prior art as described in Japanese Patent Examined Publication No. 30513/1973, Japanese Patent Publication Laid-open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 4241/1977 and No. 46558/1979, Japanese Patent Examined Publication No. 11945/1981, and the like. However, these azo compounds are not necessarily satisfactory in the speed, residual potential or stability when repeatedly used, and in addition, the carrier transport material selectable range may be restricted, so that it is the actual situation that there have not been obtained any materials that can meet sufficiently the extensive needs of the electrophotographic process.